Carbonylation of olefins to produce oxygenated products such as esters, acids, etc. is a well known process and one which is practiced commercially for the production of low molecular weight acids such as acetic acid.
Carbonylation catalysts are also known in the art as shown by an article in J. Org. Chem., Vol. 38 (1973), No. 18 p. 3192 which describes studies of the effect of several variables on a palladium-phosphine catalyst for use in carbonylation. Some of the variables studied were temperature, reagents, solvents and phosphine substituents. Another article by J. F. Knifton in J. Org. Chem., Vol 41, (1976), No. 17 p. 2885 describes the production of carboxylic acid esters from linear α-olefins using a ligand-stabilized platinum(II)-group 4B metal halide catalyst exemplified by [C6H5)3P]2PdCl2—SnCl2. This reference reports the result of using a variety of palladium complexes and reported the performance of the catalyst system varied with the coordinated ligands. The reference also indicates that internal, disubstituted olefins carbonylate more slowly than linear olefins and produce a different product distribution.
Hoffman et al. in Ind. Eng. Chem. Prod Res. Dev., 1980, 19, 330-334 describes the examination of 300 combinations of nonnoble group VIII metals and halogen-free promoters as catalysts for carbonylation. An apparent optimum catalyst system of cobalt/pyridine or γ-picoline and α-octene was used to study the effect of various parameters on the carbonylation of a mixture of isomeric internal n-dodecenes. This reference describes the use of hydroformylation to produce fatty acids and “fatty type” alcohols and indicates carbonylation had not yet been used to produce fatty acid esters or alcohols commercially.
U.S. Pat. No. 4,960,926 describes a catalyst system for carbonylation comprising a palladium compound such as palladium acetate, an organic phosphine, a non-carboxylic or non-halogen acid with a pKa of <2, a promoter and a catalyst stabilizer. The reference indicates the unsaturated compounds in the feed stream which are converted in the reaction can be cycloalkenes. An article in Journal of Organometallic Chemistry, 455 (1993), 247-253, describes the effects of different ligand structures and acid types in what appears to be a similar catalyst system.
U.S. Pat. No. 5,254,720 describes a process for producing aliphatic carboxylic acids or their alkyl esters using a catalyst system comprising palladium and copper compounds, at least one acid stable ligand, and an acid such as hydrochloric acid. This reference also indicates an optional solvent may be present in the reaction zone and lists as possible solvents a variety of ketones including acetone and aromatic hydrocarbons including xylenes. U.S. Pat. No. 5,869,738 issued to L. R. Pan et al. describes another carbonylation catalyst system comprising a Group VIII metal such as palladium or palladium chloride supported on a carrier, a ligand such as triphenylphosphine and an acid such as an alkyl sulfonic acid. The reaction may be carried out in an inert organic solvent. Mentioned solvents include an aliphatic hydrocarbon e.g. octane, an aromatic hydrocarbon such as benzene or a halogenated hydrocarbon such as chloroform or a mixture of these.
U.S. Pat. No. 5,866,716 discloses a halogen-free catalyst system consisting of a rhodium compound and at least one nitrogen containing heterocyclic compound. A large number of heterocyclic compounds are enumerated including pyridines, quinolines and imidazoles. Finally, U.S. Pat. No. 5,731,255 discloses a carbonylation catalyst system, a Group VIII metal sources, a ligand such as triphenylphosphine and an acid such as alkyl-sulfonic acid.
U.S. Pat. No. 6,646,159 B2 discloses a process for preparing alcohols and acids from paraffins. The catalyst used in the process is a palladium compound plus a LiI promoter and an organic acid such as formic acid.
In contrast to this art, applicants have developed a carbonylation catalyst comprising a palladium triphenylphosphine or a palladium imidazole complex in combination with HCl and a solvent selected from water, an alcohol and mixtures thereof. The advantages to this catalyst is that because it does not use promoters such as iodide compounds in conjunction with acids such as formic acid, one can use stainless steel to fabricate the reactors instead of more costly zirconium.